Life seemed nearly perfect for Catherine and John Graves, who married in 2001 and lovingly merged two families that included six children.
The couple also joined forces in a masonry business in Phoenix and looked forward to a bright economic and emotional future.
But just a few years into their new marriage, John Graves showed signs of having an affair. He seemed to lose interest in his wife, squandered company money and disappeared for hours at night.
Catherine Graves, now 45, even hired a private detective. But it wasn't another woman who was the problem -- it was an aggressive and fatal brain tumor that had slowly caused personality changes and eventually killed her husband of only five years.
"I faced a harsh reality," she said. "I thought I would be spending the rest of my life with him."
Graves said the crumbling marriage and then the exhausting care-giving that followed also caused her to lose her mind, a phenomenon that is all too common when family members are left without support to care for sick and dying loved ones.
Graves chronicles her own grief and guilt as a caregiver in her memoir, "Checking Out: An In-Depth Look at Losing Your Mind."
"The mental part of it was the hardest," she told ABCNews.com. "I was so depressed, but I couldn't be depressed because it wasn't about me. I was lonely and scared and the person that I knew had vanished."
One-third of all American adults are taking care of their ill or disabled relatives and that number is expected to grow.
And an estimated 70 percent of all caregivers are women, according to Richard Nix, executive vice president of Aging Care, a website that provides resources and an online community.
"The point is caregivers are trying to hold it all together and don't have the time to go to support groups," Nix said.
Another study from the American Psychological Association found that caregivers like Graves are more likely to report more stress than the general population and at higher risk for chronic illness themselves.
Graves said she stayed strong during the five months she cared for her husband. But after his death in 2007, Graves declined into depression and anxiety and was eventually treated for post-traumatic stress.
"First of all, we had a year of a really horrible marriage -- he went from loving me more than anything in the world to seeming like he didn't care about me at all," Graves said.
When the private detective turned up nothing nefarious, the couple sought counseling and John was diagnosed with depression.
But after he suffered a seizure while in residential treatment, counselors sent him off to a hospital emergency room where a brain scan revealed a virulent glioblastoma, commonly called a glioma.
There are more than 120 types of brain tumors, according to the National Brain Tumor Society, and personality changes can accompany a glioma, depending on its location and size in the brain.
"It's not typical, but it can happen," said Dr. Dan Barrow, chairman of the department of neurosurgery at Emory University School of Medicine in Atlanta.
One of the most infamous cases was Charles Whitman, the so-called Texas Sniper. The University of Texas student killed his wife and mother, then killed 13 others shooting from a tower in Austin in 1966; 33 others were wounded.
After an autopsy, doctors revealed he had glioma blastoma. "Indeed, much of his behavior was attributed to that," said Barrow.
"It's not rare for people with brain tumors to present, among other things, a personality change," said Barrow. "Sometimes it's subtle and noticed only by loved ones."